Environmental Engineering Reference
In-Depth Information
temperatures since the mid-twentieth century is very likely due to the observed
increase in anthropogenic greenhouse gases, with an assessed probability of
occurrence [90%, while high grades of probability and confidence are also
attributed to the effect of global warming on ecosystems, economic sectors and
geographical regions [
50
].
The estimation of future climate changes is also object of debate, and has been
analyzed by IPCC on the base of different emission scenarios. The results of these
analysis evidence that if carbon dioxide emissions will continue to increase at the
current growth rate for anthropogenic causes (about 3%/year) its atmospheric
concentration will reach about 1100 ppm by 2100 (and in this case there will
remain few doubts about the severe negative effects on climate), while if CO
2
emissions will be controlled maintaining the current annual level, they will be
about 520 ppm in the atmosphere by 2100. In the contest of these scenarios, many
climate models have been used to individuate an acceptable value for CO
2
atmospheric concentration, i.e. a value compatible with the forecasts regarding
population and energy demand increase. A part from the different values proposed
as CO
2
concentration level to be stabilized (ranging from 450 to 550 ppm by
2050), there is agreement among researchers that this stabilization cannot be
achieved only by the improvement of current energy technologies, prevalently
based on fossil sources, although they are becoming continuously more efficient.
On the other hand, some proposed solutions about the possibility to solve the
problem of CO
2
emissions by sequestration of this gas in ''safe'' sites, such as
disused mines or oil wells and seabeds, are very energy demanding and still in an
initial stage of development [
51
]. As a consequence, it is a generally established
opinion that an acceptable value of CO
2
concentration in the atmosphere can be
reached by the mid-21st century only thanks to the implementation of energy
carriers generated from nuclear or renewable resources.
It has been already discussed before that electricity and hydrogen, produced by
carbon-free resources, can be regarded as clean energy carriers to be used in both
stationary and mobile applications. In particular, BEVs and HFCEVs represent the
fundamental instruments towards the implementation of alternative energy carriers
in a key sector such as that of transportation means. However, as any evaluation
regarding the employment of alternative energy sources cannot leave efficiency
issues out of consideration, the potential of BEVs and HFCEVs has to be assessed
and compared in terms of global efficiency, i.e. by ''well-to-wheels'' analysis, with
the two types of vehicles using fossil fuels—internal combustion vehicles (ICVs)
and hybrid thermal electric vehicles (HTEVs). In the latter, thanks to hybridization,
the internal combustion engine can be designed for the mean power of a typical
driving cycle instead of the maximum power required, allowing the engine to
operate in conditions closer to those of its optimal efficiency (details on working
characteristics of vehicles using electric drives are discussed later, in
Chap. 5
).
When this evaluation is effected for vehicles powered by different energy carriers,
it is necessary to consider the primary energy utilization efficiency as a measure of
comparison, in order to take into account the entire amount of energy involved from
the ''well'' to the ''wheels''. Starting from an amount of any primary energy (the
